I am filling up application form for IIT kanpur.What do we need to select in preference?

Why are they asking for preference? It should matter for research .But for M.tech(TA) person it should be same. Most of you have filled this up.Does this preference has any role to play?I think they will take one common test?Or will there be test based on preference?Please help.The student who will be selected based upon test will have same course structure?